AbstractEleven males with fragile X syndrome [fra(X)] between the ages of 6 and 41, with an average communication age of 4 years 4 months and 11 normally developing 4 year old boys were administered a sentence completion task that assessed expressive semantic competence. The fra(X) males produced significantly more semantic errors than the normally developing 4 year children. Additionally, it was shown that sentences which could be correctly completed by a wider choice of words affected fra(X) males more than the nondisabled children. These 2 results suggests that the expressive semantic system is an area of specific deficit in fra(X) males.